Day 21 part 1

2 files changed, 43 insertions, 0 deletions

diff --git a/inputs/day_21.txt b/inputs/day_21.txt
new file mode 100644
index 0000000..bfb2937
--- /dev/null
+++ b/inputs/day_21.txt
@@ -0,0 +1,2 @@
+Player 1 starting position: 7
+Player 2 starting position: 5
diff --git a/src/bin/day_21.rs b/src/bin/day_21.rs
new file mode 100644
index 0000000..e937bcb
--- /dev/null
+++ b/src/bin/day_21.rs
@@ -0,0 +1,41 @@
+use nom::{
+    bytes::complete::tag,
+    character::complete::u32 as nom_u32,
+    combinator::map,
+    sequence::{preceded, tuple},
+    IResult,
+};
+use std::fs;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("inputs/day_21.txt")?;
+    let mut player_positions = parse_starting_positions(&input).unwrap().1;
+    let mut player_scores = [0, 0];
+    let mut dice = (1..=100).cycle().enumerate().peekable();
+    let mut player_turn = 0;
+    while player_scores[0] < 1000 && player_scores[1] < 1000 {
+        let dice_roll: u32 = dice.by_ref().take(3).map(|(_, roll)| roll).sum();
+        player_positions[player_turn] = (player_positions[player_turn] + dice_roll) % 10;
+        if player_positions[player_turn] == 0 {
+            player_positions[player_turn] = 10;
+        }
+        player_scores[player_turn] += player_positions[player_turn];
+        player_turn = (player_turn + 1) % 2;
+    }
+    let losing_score = player_scores.iter().min().cloned().unwrap_or(0);
+    let dice_roll_count = dice.peek().unwrap().0;
+    dbg!((losing_score, dice_roll_count));
+    dbg!(losing_score * dice_roll_count as u32);
+
+    Ok(())
+}
+
+fn parse_starting_positions(input: &str) -> IResult<&str, [u32; 2]> {
+    map(
+        tuple((
+            preceded(tag("Player 1 starting position: "), nom_u32),
+            preceded(tag("\nPlayer 2 starting position: "), nom_u32),
+        )),
+        |(a, b)| [a, b],
+    )(input)
+}